With the improvement of the level of modernization of the national economy and the increase of urban population, the contradiction between land occupation caused by residence and all kinds of activities of the human is increasingly intensified. From a macro point of view, the problems of human living spaces caused by the increase in population, the growth of living needs, the increasing deterioration of lands and other natural conditions and the gradual depletion of resources have reached to the extent of a crisis. In this case, the development and comprehensive utilization of underground space resources provide natural resources with huge potentials for the expansion of human living spaces.
However, in the development and utilization of underground space, it is necessary to classify the surrounding rock types of engineering and support excavated rock masses according to the relevant classification conditions of the surrounding rocks. If the excavated rock masses are not appropriately supported, engineering accidents such as the collapse of the surrounding rocks will happen, resulting in huge economic losses and also bringing threats to the life safety of construction workers. Therefore, the accuracy of the classification of the surrounding rocks and the feasibility of the geotechnical engineering support design are of great significance to ensure the construction safety of the engineering and save the economic cost of the engineering. In the process of classification of the surrounding rocks and the support design, the accurate selection of shear parameters of the rock masses plays an important role.
In the underground engineering, the rock mass will generate a dilatancy phenomenon in a shear process of discontinuities, and this dilatancy will be constrained due to the presence of the surrounding rock masses. The so-called discontinuities can also be referred to as a structural surface, including joints, cracks, faults and other conditions. As the discontinuity is rough and uneven, with the increase of the shear displacement and the continuous change of the dilatancy degree, the normal load of the surrounding rock masses on the discontinuity will also change continuously. In the process, only the stiffness of the surrounding rock masses remains constant.
The existing shear test machines can only achieve a constant load boundary, and this boundary condition can only simulate engineering conditions in which normal loads acting on discontinuities are unchanged, such as unsupported slopes. Both the rock mass in the underground engineering and the rock mass under anchoring conditions are under the boundary condition of constant normal stiffness, therefore the constant load boundary condition is not suitable for such engineering conditions anymore. The existing shear test machine cannot well simulate such engineering conditions.
In addition, existing shear test devices only consider the normal stress state, and cannot apply the required shear load under the condition of simulating the primary rock stress of the rock mass.
The above shortcomings of existing test shear instruments will cause the distortion of a simulation environment, resulting in greater difference between the obtained mechanical parameters and the actual situation, and even resulting in wrong determination of the classification of the surrounding rocks, misleading the reasonable selection of the excavation method and the support design, causing serious hidden troubles to construction safety or causing unnecessary waste of engineering economic costs.